EA4 - MPM Worker w/ PHP 7 - 500 Error

I'm having an issue after upgrading to EA4 and enabling MPM Worker w/ PHP5.6 and PHP7. When our site is using php 5.6 it seems to work just fine. When I switch the site to PHP 7 we get "500 Internal Server Error". I can't seem to find any useful logs telling me what is causing this. Any ideas? Any log files that would tell me the PHP error(s)?

'/var/log/apache2/error_log' will tell you why it's throwing an error. If you have to start debugging PHP, start by comparing PHP configurations between the two versions. A low memory_limit amongst other things could cause these issues.

For some reason that log didn't help me. I was able to use Symfony 3's debuging tool and saw that my SOAP functions were throwing errors. Needless to say, when you upgrade to PHP7 be sure to delete your WSDL cache's!